Molded product and method of manufacture

ABSTRACT

A molded product is made comprising a low-density product having an impermeable surface. The impermeable surface integral with the low density interior is suitable for receiving various types of brightly colored finishes. It is also contemplated that a non-porous plastic film may be molded in place on the surface of the molded product.

This application is a divisional of U.S. Application Ser. No. 08/734,900filed Oct. 22, 1996, now U.S. Pat. No. 5,736,075.

TECHNICAL FIELD

This invention relates generally to molded objects and methods ofmolding. It particularly concerns an object molded of foam materialwhich has many of the characteristics of a solid molded object, andmolding methods for achieving such characteristics.

BACKGROUND OF THE INVENTION

Toys and other objects which are fabricated from porous materials suchas foamed plastics have certain advantages: they are light in weight,owing to their low density; and they are safe for children, owing totheir compressibility. Such lightness, safety and compressibility makesthese materials especially suitable for bouncing balls, flying toys suchas gliders, and throw-toys such as darts. But these materials have notgenerally produced very good results when used for other types of toysand other products.

In the past it has been difficult or impossible to fabricate suchmaterials in a form which is acceptable to the marketplace. Foammaterials are usually supplied in sheet form, making it difficult tofabricate them into objects of non-uniform thickness. By comparison,injection-molded plastic objects can be made in a wide variety of shapesof non-uniform thickness. Injection molding also has been favored forthe inclusion of molded-in-place inserts of various types. Historically,foam materials have not held such inserts well.

In addition, the toy marketplace favors objects with a shiny surface,preferably decorated with a variety of bright colors. Foam materialshave heretofore had a dull, porous surface which is unsuitable forfinishing with brightly colored paints, silk screens, tampo printing anddecals. Such surfaces are also unsuitable for the molding of finesurface detail, which lends a desirable realism to toy objects. Anotherproblem encountered with foam objects of the prior art is theirvulnerability to tearing because of the softness of the surface layer.

The present invention, however, contemplates the molding of toys andother objects from foam materials, yet provides such objects with atough, smooth, shiny surface which is similar to that which results frominsert molding. As a result, the molded foam objects of this inventioncombine foam's advantages of lightness, safety and compressibility witha superior ability to hold molded-in-place inserts and to accept varioustypes of surface decorations, preferably brightly colored, plus finesurface detail. The molded foam objects of the invention are also moredurable, because the tough surface layer resists tearing.

BRIEF SUMMARY OF THE INVENTION

These desirable results are achieved by a method of molding alow-density object having an impermeable surface, from porous material,comprising the steps of preparing a mold having a cavity the outline ofwhich defines the outline of the object, stamping from the porousmaterial a blank having substantially the outline of the object,inserting the blank into the cavity with the outline of the blanksubstantially congruent with the outline of the cavity, heating the moldwith the blank therein to form the blank permanently into a product, andthen removing from the mold and freezing the product, the durations andtemperatures of the heating and freezing steps being chosen such that animpermeable surface is permanently formed on the product, whereby theproduct has the appearance of having been formed from non-porousmaterial.

In a most preferred form of the invention, after heating the mold isquenched in cold water, after which the molded product is removed andsubjected to freezing.

The result of this molding method is a low-density product having animpermeable surface and a foam interior integral with the impermeablesurface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exploded perspective view of a sheet of foam plasticmaterial, from which a number of mold blanks have been cut and removed;

FIG. 2 is a perspective view of a double mold designed to receive two ofsaid blanks;

FIG. 3 is an elevational view of a heating chamber through which anumber of said molds are passed, thereby molding the blanks into desiredobjects;

FIG. 4 is a vertical sectional view of a cold-water-filled quenchingchamber used for subsequent rapid chilling of said molds with the moldedproducts therein;

FIG. 5 is a vertical sectional view of a freezer used for subsequentlyfreezing the molded products;

FIG. 6 is a front elevational view of one of the finished moldedproducts;

FIG. 7 is an enlarged sectional view of a portion of the surface layerof the finished molded product.

FIG. 8 is a perspective view of another type of finished product whichcan be made in accordance with the present invention, which is in theform of a hollow shell;

FIG. 9 is a perspective view of a mold used for making the product ofFIG. 8 in accordance with this invention;

FIG. 10 is a vertical sectional view of the mold of FIG. 9; and

FIG. 11 is a perspective of a conveyer oven used in making the productof FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The molding process of this invention begins with conventional plasticmaterial formed of foamed poly-ethylene (PE) or foamed poly-ethylenevinyl acetate (EVA), both of which are commercially supplied in the formof a flat sheet 10 of uniform thickness (i.e., in the verticaldirection, as seen in FIG. 1). The standard commercially available sheetsize is 100 cm. by 200 cm.; and the available thicknesses range from 3to 100 mm., the thickness being substantially uniform across the lengthand breadth of any particular sheet. The density of such materials iscomparable to that of rubber at ordinary ambient temperatures.

The objective of the process is to produce a toy or other end product 12(FIG. 6) which in general has a non-uniform thickness in all dimensions,notwithstanding the uniform thickness of the commercially availablesheet stock.

The first step in the process is to die-stamp from the foam sheet 10 oneor more mold blanks 12A, B, C, etc. which have an outline roughlycongruent with the intended outline of the final product 12. Because thestamping die cuts through the entire thickness (in the verticaldirection) of the foam sheet 10, no flash or parting line results fromthe die-cutting process. In FIG. 1 the first blank 12A is shown afterhaving been lifted out of the foam sheet 10. At this stage of theprocess, the blanks 12A, B, etc. have the same uniform thickness (in thevertical direction) as the sheet 10 from which they came.

The next step is to put one or more blanks 12A, B, etc. into suitablehalf cavities such as 14A, B formed in the lower half 14 of a metalmold. Connected to the lower half 14 by hinge 16 is an upper half 18 ofthe metal mold, which is formed with complementary half cavities 18A, B.After the foam blanks 12A, B, etc. are inserted into the lower cavities14A, B, the upper half 18 is rotated about the hinge 16 to close themold, and the mold is then clamped closed by means of a conventionalclamping mechanism, part of which is visible at 20.

When the mold is closed, the upper half cavities 18A, B cooperate withthe lower half cavities 14A, B to form complete molding cavities whichcompletely enclose the foam blanks 12A, B, etc. The outlines of theupper and lower half cavities are congruent with each other, and withthe desired outline of the final product 12.

The concave surfaces of the half cavities have the external surfaceshapes of the upper and lower portions respectively of the desired finalproduct, and thus serve to mold the blanks 12A, B into products 12 ofthe desired final shape. That shape will generally have a non-uniformthickness, even though the foam blanks previously were of uniformthickness, like the foam sheet 10 from which they were stamped. Inaddition, the concave surfaces of the half cavities are engraved withfine surface relief detail which is to be impressed upon the surface ofthe final product 12.

The closed mold 14, 18, with the foam blanks 12A, B, etc. inside thecavities 14A, 18A and 14B, 18B is then passed through an oven 22 mountedon a table 24. Movement of the molds through the oven may be eitherintermittent or continuous, and may be accomplished either manually orby means of a conventional automatic conveyer mounted on the table 24.The temperature inside the oven 22 is in the range from 200 to 300° C.,and the duration of exposure to the oven temperature is in the rangefrom about 5 to about 15 minutes.

After emerging from the oven, the molds 14, 18, with the foam blanks12A, B, etc. still inside, are immersed in a vat 26 of cold water 28 forthe purpose of quickly chilling the surface of the foam blanks wherethey contact the concave surfaces of the cavities 14A, 18A and 14B, 18B.The relatively high heat conductance of the metal mold 14, 18facilitates rapid cooling of the surface layer of the mold blanks 12where they contact the mold. The temperature of the cooling water is inthe range from about 5 to about 20° C., and the duration of exposure tothe chilling water is from about 5 to about 15 minutes.

Subsequently the molds 14, 18 are removed from the water bath 28, openedby releasing the clamps 20 and rotating the upper mold half 18 away fromthe lower mold half 14 about hinge 16, and the molded objects 12 arethen removed from the molds and placed in a freezing compartment 30 byinserting the objects 12 through a door 32 and placing them on shelves34 inside the compartment 30, after which the door 32 is closed. Thefreezer temperature is from about −5 to about −15° C., and the durationof exposure to the freezing temperature is in the range from about 30 toabout 45 minutes.

The EVA foam starting material used in the present invention isclassified as “closed cell,” which means only that the cells do notconnect with each other; the cells do, however, open through theexternal surface of the sheet 10, making the surface dull-looking andporous. The PE starting material is classified as “open cell,” and alsohas a dull and porous external appearance because of the fact that thecells open through the surface.

The process of this invention produces a substantially lower reject ratethan prior processes for molding foam products, which have tended tosuffer from irregularities in shape and finish, and incorrect andinconsistent control of softness and density. In addition, prior artproducts molded from foam materials were characterized by dull andporous surfaces which have defied efforts to apply bright and colorfulfinishes; those finishes which were applied tended to peel off easilyand did not achieve a bright, shiny or colorful effect. The surfacedetail was also poor.

But, as seen in FIG. 7, the result of the successive hot molding, coldquenching and freezing steps of this invention is to create a layer 12Lat the surface of the final product 12 in which the cells or pores 12Pare sealed and do not open up through the surface of the final product12. Indeed, the surface now consists of a tough, smooth, impermeableskin 12S, which has substantially the same characteristics as thesurface of an injection-molded product: i.e., it is tough, smooth,shiny, durable, and able to receive and hold various types of decorativefinishes.

The finished product 12 is also better able to hold molded-in-placeinserts, and is less likely to be torn in use. The surface 12S also hasa smooth, shiny finish which is inherently more attractive than thedull, porous look of untreated foam materials; which holds fine detailin a way which has not previously been accomplished with foam materials;and which also lends itself to various finishing processes involvingbright and decorative colors.

In particular, the finishing processes which have been found to workwell in the method of this invention are color die spraying, tampoprinting, silk-screening, and the use of a non-porous PE filmpre-printed with graphics or a solid color and laminated with a gluewhich causes the films to adhere to the surface of the product 12. It isa particular feature of the invention that such films can be applied tothe mold blank 12 before the heating step of FIG. 3, in which case thefilm is permanently molded in place on the surface of the product 12.

At the same time, the bulk of the product 12, below the surface layer12L, retains the original porosity and hence the low density of theoriginal foam sheet 10. As a result, the final product remains soft,light, flexible, and therefore safe for use as a glider, dart toy,bouncing ball, or the like. In addition, the final product 12 can haveany desired non-uniform thickness, despite having been formed from asheet 10 of uniform thickness.

In accordance with an additional aspect of this invention, it issuitable for molding shapes having the general configuration of a hollowshell, such as the toy car body 40 illustrated in FIG. 8, which featuresa hollowed-out interior space 40A. This type of configuration isproduced by means of the mold 42, which has a lower mold half 44 formedwith a convex core 44A and an upper mold half 46 formed with acomplementary cavity 46B. A hinge 48, guide pins 50 on the lower moldhalf 44, complementary guide holes 52 on the upper mold half 46, and alatching mechanism 54, 56 complete the mold assembly.

The sectional view of FIG. 10 illustrates the hollow shell-like shape 40being formed within the closed mold 42. In order to permit a bulky massof foam material cut from the sheet 10 to be more easily compressedbetween the core 44A and cavity 46A for molding purposes, it ispreferable to heat the foam material at a temperature of about 200° C.for about 3 to about 5 minutes in order to soften the material beforebeginning the molding process. For this purpose, an oven 60 (FIG. 11) isprovided, and is equipped with a conveyor belt 62 which transportssheets of foam material 10 through the oven prior to their undergoingthe process steps described above. Alternatively, this pre-heatingprocedure may be performed on the foam blanks after they are stampedfrom the sheet 10; but the stamping is facilitated if the pre-heatingstep is done first, so that the sheet material 10 is softer at the timethe blanks are stamped out.

The ability to mold hollow shell-like configurations as just describedopens up the possibility of using the process of this invention tomanufacture a wider variety of products, not all of which are toys. Forexample, inexpensive soft-sided luggage-like containers with attractiveexterior finishes may be manufactured in this manner, as well asprotective shock-absorbing housings, cases or covers for smallelectronic appliances, books, and a wide variety of other objects.

Despite somewhat higher raw material costs, the present inventionachieves certain significant economies as compared to other moldingprocesses. First, the molds employed in injection molding processes atevery expensive. In order to withstand the high temperatures employed ininjection molding, the molds must be made of expensive steel; whereas inthe present process a much less expensive aluminum alloy material isadequate. In addition, injection molding requires numerous conduits andfittings to conduct the molten plastic resin into the mold cavity; allof which is unnecessary with the process of this invention.

As a result, the mold cost, which can run around $40,000 per cavity foran injection mold, is reduced to the neighborhood of only $2,500 percavity. This permits the construction of a greater variety of molds fora given cost; which is advantageous generally, but particularly in thetoy field because it permits a manufacturer to satisfy consumer desiresfor greater product variety.

Second, the fact that products manufactured in accordance with thisinvention can be finished with multi-colored pre-printed PVC film offersa significant saving over other finishing processes requiring moreindividualized attention to each manufactured piece.

Accordingly, the present invention, in both its process and productaspects, economically produces a flexible, light, shiny, brightly andcolorfully finished, durable product of any desired cross-sectionalshape. While these features and advantages of the invention have beendescribed in connection with a preferred illustrative embodiment, thescope of protection to which the invention is entitled is to bedetermined by the appended claims, interpreted in light of the novelprinciples disclosed herein.

The invention claimed is:
 1. A low-density product having a non-uniformcross-section and a sealed impermeable surface, said product and itssurface both having been formed from the same sheet of pliablepolyethylene based foam material of substantially uniform cross-section.2. A low-density product formed of pliable polyethylene having anon-uniform cross-section, a smooth impermeable surface, and acompressible foam interior integral with said impermeable surface.
 3. Aproduct as in any of claims 1, or 2, further comprising a decorativecoating on said impermeable surface, said coating formed by applying aliquid material to said surface.
 4. The low-density product of claim 2wherein said smooth impermeable surface includes an ornamentalbase-relief detail.
 5. A low-density product formed of a single sectionof compressible polyethylene or ethylene vinyl acetate copolymer foamhaving a relatively low density interior and a relatively higher densityouter surface surrounding said low density interior and integrallyformed therewith, said higher density outer surface being substantiallyimpermeable to liquids, said product having been formed into anirregular shape having variable vertical, lateral, and horizontal crosssections.